The purpose of the study is to determine whether orally-administered 13C-labeled L-2-oxothiazolidine-4-carboxylic acid (OTC) could act as a probe for glutathione (GSH) status in the human. During the reporting period, two volunteers were studied with two tests each. Analysis of the data suggest that acetaminophen ingestion, which lowers hepatic GSH stores, is associated with increased 13CO2 excretion in breath. The 13C-label enters the bicarbonate pool after hydrolysis of OTC to produce cysteine, the rate-limiting amino acid in GSH synthesis.